1. Field of the Invention
This invention relates to methods for removing atherosclerotic plaque, and in particular, pertains to a method of precise guidance for directional atherectomy for more complete removal of plaque.
2. Description of the Related Art
Angiography is the visualization of blood vessels after injection of a radiopaque substance. Angiography is often used to show the location and number of plaque sites, as well as the length of the plaque area and the severity of the plaque problem. In addition, angiography may be used prior to atherectomy to measure the lumen diameter inside the accumulated plaque in the vessel. The plaque cutter size is normally chosen to fit within this lumen to minimize the likelihood of perforation of the vessel wall, since angiography does not allow one to determine the actual interior dimensions of the vessel itself. The previous inability to detect appropriate removal of atherosclerotic plaque from the coronary vessel wall using angiography has been a limiting factor in the use of many atherectomy devices.
After the plaque location is known, plaque removal from blood vessels is generally accomplished using atherectomy. Many types of device for performing atherectomy have been devised.
A basic atherectomy catheter device (U.S. Pat. No. 4,411,055 of Simpson and Robert) utilizes a guiding catheter assembly in which a first tubular member is encased by a second tubular member. A dilating catheter assembly can be inserted into the guiding catheter assembly. U.S. Pat. No. 4,669,469 of Gifford and Simpson discloses a cutter mounted in a cylindrical housing which has a single luminal opening, and a flexible drive cable. An inflatable balloon is positioned outside the housing opposite the cutout, and a medium for inflating the balloon is introduced through the luminal opening of the catheter.
The blade for doing the cutting may be simply positioned in the tip of a vascular catheter to be extendable transversely when the catheter is in the correct position (U.S. Pat. No. 5,053,044 of Mueller et al.). Cutters for atherectomy devices include helical cutting blades (for example, U.S. Pat. No. 5,226,909 of Evans et al.), rotatable cylindrical cutting heads (U.S. Pat. No. 5,242,460 of Klein et al.).
The atherectomy device of Simpson (U.S. Pat. No. 4,979,951) has a generally cylindrical, relatively rigid housing with rounded distal and proximal end portions. The housing has a longitudinal cutout, inside which is disposed an atheroma cutter. A flexible drive cable extends through the flexible guide, and is connected to the atheroma cutter for operation of the atheroma cutter.
The catheter of Gifford et al. (U.S. Pat. No. 4,926,858) has a distal cutter assembly and a proximal actuator assembly for imparting both rotary and axial movement to the cutter. A retention member carried by a guide wire is positioned in front of the cutter and forms a cap to retain collected atheroma materials.
The patent of Mueller et al., U.S. Pat. No. 5,181,920, is for a device with an elongated flexible tubular member with a distal cutting assembly and having a flexible drive means within the tubular member which has a distal cutter. An inflatable dilation balloon is carried by the tubular member proximal of the cutter so that a stenosis may be dilated immediately prior to or after cutting the stenosis. Numerous balloon configurations for catheters have been devised. See, for example, U.S. Pat. Nos. 4,748,982 of Horzewski et al.; 5,092,873 of Simpson and Muller; 5,041,089 of Muller et al.; and 5,117,831 of Jang et al.
The vascular catheters used for atherectomy utilize various guide wire systems for introducing the catheters into the vascular systems. See, for example, U.S. Pat. Nos. 5,040,548 and 5,061,273 of Yock; U.S. Pat. No. 5,269,793 of Simpson; and U.S. Pat. No. 5,201,316 of Pomeranz et al.
For use of most types of cutter, fluoroscopy using X-rays allows visualization of the radiopaque cutter used to remove plaque formations. The cutter may be rotated while viewing with fluoroscopy to optimize the position of the cutter with respect to the plaque location.
Ultrasound allows visualization of the cross-section of the plaque. Ultrasound imaging catheters allow over-the-wire imaging of the catheter as the cutting process proceeds. Thus, one ultrasonic apparatus of Yock (U.S. Pat. Nos. 4,794,931 and 5,000,185) includes an ultrasonic transducer carried by the distal end of a catheter. Either the transducer or another element is rotated or translated relative to the catheter to image different portions of the vessel for intravascular imaging. A fixed ultrasonic transducer may be used to direct ultrasonic energy at a reflective surface on a rotating element which allows the interior of the blood vessel to be scanned prior to the application of laser energy to ablate the obstruction (U.S. Pat. No. 5,029,588 of Yock et al.).
The ultrasonic imaging catheter of Scribner et al. (U.S. Pat. No. 5,054,492) comprises a catheter body with an ultrasonic imaging transducer located within the distal end, and arranged to produce an image in an image plane which is normal to the axial direction of the catheter. An ultrasonically opaque element is attached to the catheter body and disposed through the image plane so that an image marker appears on the resulting ultrasonic image, corresponding to the location on the catheter where the element is located, relative to a fluoroscopic marker on the catheter itself. This allows the actual rotational orientation of the catheter within the body lumen being viewed to be known.
An ultrasonic imaging means may be affixed to an abrasive rotatable head which is used for removal of intravascular plaque (U.S. Pat. No. 5,100,424 of Jang et al.). Other ultrasonic imaging systems include, for example, U.S. Pat. No. 5,203,338 of Jang; U.S. Pat. No. 5,209,235 of Brisken et al.
Although ultrasound is potentially well suited to augment angiography in guiding directional atherectomy, the orientation of cuts based on identification of branch vessels common to both the ultrasound and the angiographic images lack precision and can be quite time-consuming. Although ultrasonic imaging allows visualization of the interior of the actual vessel, even if the vessel has an interior plaque layer, and fluoroscopy allows visualization of the cutter, it is not possible to view both the plaque and the cutter as the cutter is operated. Therefore, it is difficult to perform the cutting accurately so that the desired quantity of plaque is removed without perforation of the vessel wall. Because the plaque may be uneven, or the cutting may begin off-center of the vessel, even very gradual removal of plaque in a gradually increasing circle around the apparent vessel center may result in perforation of the vessel on one side of the vessel before plaque is entirely removed.
It is therefore an object of this invention to provide a method of visualizing plaque removal as the removal process proceeds to allow substantial plaque removal from the vessel at minimal risk of wall perforation.
It is a further object of this invention to provide a method of determining cutter size based on actual vessel size (the size of the vessel without the plaque) rather than on plaque lumen size and utilizing larger cutters sized to the actual vessel size, without increasing the likelihood of vessel wall perforation during the plaque removal process, which is contrary to what would be expected with the use of a larger cutter.
It is a further object of this invention to provide a method of removing plaque which combines the strengths of both angiography and ultrasound imaging to more effectively guide directional atherectomy for more complete removal of plaque from native coronary arteries.
It is a further object of this invention to provide a method which allows about 90% plaque removal from outside the body using atherectomy catheters for essentially any vessel without increased risk of perforation or with decreased risk of perforation.
Other objects and advantages will be more fully apparent from the following disclosure and appended claims.